6. Cell Division

• Interphase - G0, G1, S, G2
• Cell cycle

  a series of events when a parent cell divides to form a daughter cell
• G0

  Senescence (no longer dividing)
• G1

  Protein synthesis, cell components except for chromosomes are duplicated.
• G2

  Second growth phase - organelles increase in number.

  DNA condenses.

  Energy stores increased.

  Duplicated DNA is checked for errors.
• Interphase

  Preparation for mitosis.

  Producing hormones, enzymes, and actively preparing for cell division.
• Synthesis stage

  Replication of DNA
• Why G0?

  Differentiation, cell damage, link to age related diseases.
• Checking DNA:

  Prevent uncontrolled cell division, detect and repair damage to DNA.
• Prophase

  Chromosomes condense, centrioles move to opposite ends of the cel, forming spindle fibre. The nuclear envelope breaks down and chromosomes lie free in the cytoplasm.
• Metaphase

  Chromosomes line up along the middle of the cell and attach to spindle fibres by centrioles.
• Checkpoint in Metaphase

  The cells checks that all chromosomes are attached to the spindle fibres before mitosis can continue.
• Anaphase

  Centromeres divide and spindle contract, pulling chromatids to opposite ends of the cell.
• Telophase

  Chromatids reach opposite poles and uncoil, becoming long and thin again, now chromosomes. Nuclear envelope forms around each group of chromosomes.
• Cytokinesis

  Usually begins in anaphase and ends in telophase.

  Cytoplasm divides and there are now two genetically identical daughter cells.
• Importance of mitosis

  Growth, asexual reproduction, and repair.
• Mitosis

  Nuclear division that results in the formation of cell that are genetically identical to the parent cell.
• Mitosis

  Nuclear division that results in the formation of cell that are genetically identical to the parent cell.
• Erythrocytes

  Biconcave to increase SA.

  No nucleus for more space for haemoglobin.

  Flexible to move around tight capillaries.
• Neutrophil wbc

  Mulitlobed nucleus to squeeze through gaps.

  granular cytoplasm contains lysosomes to attack pathogens.
• sperm cell

  Male gametes deliver genetic info to ovum. Flagellum for movement, mitochondria for extra energy, acrosome contains digestive enzymes to penetrate egg.
• Palisade cell

  Present in mesophyll.

  Contain chloroplasts to absorb light for photosynthesis. Box shaped for closely packed continuous layer. Thin cell walls for short diffusion distance.
• Root hair cell

  Long extensions increase surface area to maximise water uptake.
• Guard cell

  Can change shape to prevent water loss in transpiration. Cell wall is thicker on one side so cell does not change shape symmetrically as volume changes.
• Squamous epithelium

  Thin cells for short diffusion distance.
• Ciliated epithelium

  Hair structures to waft mucus away from lungs into stomach acid to kill pathogens.
• Cartilage

  Connective tissue, contains elastin and collagen, prevents running damage.
• Muscle

  Contracts to move bones.
• Skeletal muscle fibres are attached to bones and contain myofibrils.
• Epidermis

  Single layer of closely packed cells covering plant surfaces.

  Waxy and waterproof to reduce water loss.

  contains stomata to allow substances in and out.
• Totipotent

  Can differentiate into any type of cell, e.g. embryonic stem cells.
• Pluripotent

  Can form any new tissue but not whole organisms, e.g. in early embryos
• Multipotent

  Can only form a range of cells within a certain type of tissue so adult stems cells, e.g. bone marrow gives rise to blood cells.
• Independent assortment

  In metaphase 1, homologous pairs of chromosomes are arranged randomly with members of each pair facing opposite directions.
• Independent assortment ensures that the four daughter cells have different combinations of alleles for each gene.
• Crossing over

  Where non-sister chromatids wrap around each other and may swap sections so that alleles are shuffled.
• Haploid cell

  23 chromosomes
• Diploid

  46 chromosomes